Modern well-drilling operations commonly use a drill bit, drill pipe (sometimes referred to as “the drill string”) connected to the drill bit, and rotational machinery at the surface to rotate the drill pipe, resulting in rotation of the drill bit. The drill string is extended in length by adding additional sections of drill pipe as the drilling creates an ever deeper borehole.
Materials dislodged from the bottom of the borehole by the drill bit are flushed to the surface, typically using compressed air and a liquid carrier transferred down the center of the hollow drill pipe. Water, drilling mud, and other suitable substances may be used as the liquid carrier. The carrier and compressed air are forced down the center of the drill pipe under pressure from compressors at the surface. The liquid carrier washes the cuttings away from the drill; and the liquid carrier and the cuttings are forced to the surface by the compressed air through an annulus that is typically the annulus between the outer surface of the drill pipe and the borehole wall.
As well drilling operations proceed down the borehole, reservoirs of liquids and/or gases (“effluents”) may be encountered at various levels above the final borehole depth. The effluents tend to pour to the bottom of the borehole and accumulate in the annulus between the drill string and the borehole wall, forming an approximately annular column of effluents. The column of effluents exerts both downward and lateral pressure on the drill bit assembly. Compressor and/or booster equipment at the surface must produce sufficient pressure to overcome the pressure exerted by the column of effluents as well as pressure sufficient to force the liquid carrier down the drill pipe and to force the liquid carrier and cuttings up the borehole annulus to the surface. Increasingly greater pressures must be generated at the surface to overcome the increasingly taller column of effluents as the borehole depth increases.
An additional and related problem occurs with a commonly-used “downhole hammer” type of drill bit assembly. The downhole hammer uses a pneumatic cylinder mechanism driven by the compressed air being forced down the hollow drill pipe. The downhole hammer exerts periodic bursts of additional torque and/or downward force at the drill bit to aid in drilling. Pressure from the water column impedes operation of the pneumatic cylinder, adding yet more load on the compressor/booster equipment at the surface.
The additional torque and pneumatic pressure supply are produced by larger diesel engines and a correspondingly greater consumption of diesel fuel at the surface. This ratcheting-up of torque and pneumatic pressure necessary to drill deeper may continue until a drilling rig including compressors/boosters of a particular size and power and a drill string of a particular strength are no longer capable of rotating the drill bit assembly, operating the pneumatic mechanism associated with the downhole hammer, and expelling the effluents, liquid carrier, and cuttings to the surface. This state is referred to in the water well-drilling industry as “watering out,” and indicates the maximum drilling depth possible for the drilling rig.
The phenomenon of the forces caused by upper-reservoir effluents impeding the drilling process results in the waste of precious oil and water resources. The combustion of the extra diesel fuel required to overcome these forces releases large amounts of greenhouse gases and results in a concomitant environmental impact. Millions of gallons of water are wasted as the compressed air forces water flowing from the reservoirs/aquifers to the surface and out onto the ground.